1. Field of the Invention
The present invention relates to a motor-operated stapler having a driver which reciprocates and drives out a staple toward a sheet bundle.
2. Description of the Prior Art
Heretofore, such a motor-operated stapler as shown in FIG. 11 has been known. This known stapler is provided with a forming plate 1 for forming a staple in U shape, a driver 8 for driving out the U-formed staple toward a sheet bundle 2, a link mechanism 4 which causes the forming plate 1 and the driver 3 to reciprocate, and a table having a clincher (not shown) for clinching leg portions of the staple which has pierced the sheet bundle 2.
The link mechanism 4 has a link cam 6 mounted on a driving shaft 5 and a link member 8 mounted pivotably between a pair of frames 7. At a rear portion of the link member 8 is mounted a roller R rotatably in abutment against the link cam 6. The link member 8 is urged by means of a biasing member (not shown) in a direction in which the roller R is kept in abutment against the link cam 6. With rotation of the link cam 6, the link member 8 pivots about a shaft 8A, as shown in FIG. 12.
A shaft 9 is held in an elongated hole 8B formed in a front end portion of the link member 8. As the link member 8 pivots about the shaft 8A, the shaft 9 moves vertically along elongated holes 7A formed in the frames 7. The forming plate 1 and the driver 3 are secured to the shaft 9 and move vertically with a vertical movement of the shaft 9.
The link cam 6 is formed with a home position portion 6A for keeping the forming plate 1 and the driver 3 located at their position (home position) shown in FIG. 11, an advancing portion 6B for moving the forming plate 1 and the driver 3 downward and driving out a staple, a hold-down portion 6C for holding down the driven-out staple, and a retreating portion 6D for moving the forming plate 1 and the driver 3 upward. With one rotation of the link cam 6, the forming plate 1 and the driver 3 reciprocate once up and down.
In such a conventional motor-operated stapler, plural cams, etc. other than the link cam 6 are mounted on the driving shaft 5, so even when the motor turns OFF, the rotation of the driving shaft 5 does not stop immediately due to inertia for example. For this reason it has so far be necessary that the range of the home position portion (home position zone) 6A be taken wide. For example, even with use of a motor brake or the like, one-ninth or more of the entire rotational angle (360xc2x0) of the link cam 6 is needed and a rotational angle (an angle falling under the range of the advancing portion 6B) used for drive-out becomes narrower, thus giving rise to the problem that the rotational angle range used for other controls is narrowed.
Even if an attempt is made to rotate the link cam 6 with use of a dedicated motor as a separate drive source for diminishing inertia, a wide home position zone is required due to accumulation of accuracy errors in a transfer system for transferring the rotational force of the motor to the link cam.
It is an object of the present invention to provide a motor-operated stapler which permits narrowing the range of a home position zone of a cam.
According to the present invention there is provided a motor-operated stapler including a driver adapted to reciprocate and drive out a staple toward a sheet bundle and a drive mechanism for actuating the driver, the driver being reciprocated once with rotation of a driving cam mounted on a driving shaft in the drive mechanism, characterized by further including a brake means which brakes the rotation of the driving shaft mechanically when the driver returns to a home position thereof.